Olefin polymerization catalysts containing amine derivatives

ABSTRACT

A single-site olefin polymerization catalyst is described. The catalyst comprises an activator and an organometallic compound that includes an amine derivative ligand. The catalyst is highly productive, incorporates comonomers well, and gives polymers with narrow molecular weight distributions.

FIELD OF THE INVENTION

[0001] This invention relates to a catalyst for polymerizing olefins.The catalyst contains two polymerization-stable anionic ligands, atleast one of which is an amine derivative.

BACKGROUND OF THE INVENTION

[0002] Many olefin polymerization catalysts are known, includingconventional Ziegler-Natta catalysts. While these catalysts areinexpensive, they exhibit low activity and must be used at highconcentrations. As a result, it is sometimes necessary to removecatalyst residues from the polymer, which adds to production costs.Furthermore, Zeigler-Natta catalysts typically produce polymers havinghigh densities and broad molecular weight distributions, properties thatare undesirable for some applications such as injection molding. Theyare also generally poor at controlling polymer density throughincorporation of α-olefin comonomers. Unfortunately, when comonomers areused, they are distributed in a non-uniform fashion among the differentmolecular weights that comprise the molecular weight distribution. Mostof the comonomer is incorporated into the low molecular weight polymermolecules; a more uniform incorporation would be desirable.

[0003] To improve polymer properties, highly active single-sitecatalysts, in particular metallocenes, are beginning to replaceZeigler-Natta catalysts. Although more expensive, the new catalysts givepolymers with narrow molecular weight distributions, low densities, andgood comonomer incorporation.

[0004] A metallocene catalyst consists of one or more cyclopentadienylring ligands bound to a transition metal in an η⁵ fashion. Thecyclopentadienyl ring ligands are polymerization-stable; that is, theyremain bound to the metal during the course of the polymerization. Onedisadvantage of metallocene catalysts is that they tend to produce lowermolecular weight polymers at higher temperatures.

[0005] Recent attention has focused on developing improved single-sitecatalysts in which a cyclopentadienyl ring ligand of the metallocene isreplaced by a heteroatomic ring ligand. These catalysts may be referredto generally as heterometallocenes.

[0006] In particular, U.S. Pat. No. 5,554,775 discloses catalystscontaining a boraaryl moiety such as boranaphthalene orboraphenanthrene. Further, U.S. Pat. No. 5,539,124 discloses catalystscontaining a pyrrolyl ring, i.e., an “azametallocene.” In addition, PCTInt. Appl. WO 96/34021 discloses azaborotinyl heterometallocenes whereinat least one aromatic ring includes both a boron atom and a nitrogenatom.

[0007] Metallocenes and heterometallocenes are much more expensive toproduce than the Zeigler-Natta catalysts. Therefore, further researchhas focused on developing less expensive single-site catalysts that giveadvantageous polymer properties. One approach is to use readilyavailable organic compounds that can act as polymerization-stable,anionic ligands for transition metals. For example, U.S. Pat. No5,637,660 discloses catalysts in which a cyclopentadienyl moiety of ametallocene is replaced by a readily available quinolinyl or pyridinylligand. Other inexpensive organic ligands capable of binding atransition metal may also be available. One example is hydroxylaminederivatives Hughes, et al., J. Chem. Soc., Dalton Trans. (1989) 2389,for example describe the crystal structure of organometallic compoundscontaining hydroxylamine or hydrazine derivatives bound to a titaniumcomplex in an η² fashion, but they do not describe olefin polymerizationcatalysts

[0008] In sum, new single-site catalysts are needed. Particularlyvaluable catalysts would be easily synthesized from readily availablestarting materials. These catalysts would combine the cost advantages ofZeigler-Natta catalysts with the polymer property advantages ofsingle-site catalysts.

SUMMARY OF THE INVENTION

[0009] The invention is a catalyst for polymerizing olefins. Thecatalyst comprises: (a) an organometallic compound of a Group 3-10transition metal containing an amine derivative ligand; and (b) anactivator such as alumoxane. The amine derivative ligand has the formulaRR′N—A⁻ or RR′C═N—A— where A is O, S, N—R″, or P—R″. Substituents R, R′and R″ are hydrogen or C₁—C₂₀ hydrocarbyl. The Group 3-10 metal alsocontains other ligands to fill the vacancy of the metal. The additionalligands include polymerization-stable anionic ligands and a ligand Xwhere X is hydride, halide, C₁—C₂₀ alkoxy, siloxy, hydrocarbyl, ordialkylamido.

[0010] We surprisingly found that catalysts based on amine derivativeligands are true “single-site” catalysts for olefin polymerization: theyare highly productive, they incorporate comonomers well, and they givepolymers with narrow molecular weight distributions.

DETAILED DESCRIPTION OF THE INVENTION

[0011] Catalysts of the invention comprise an activator and anorganometallic compound of the formula:

[0012] where

[0013] M is a Group 3-10 transition metal;

[0014] A is O, S, N—R″, or P—R″;

[0015] L is a polymerization-stable anionic ligand;

[0016] X is hydride, halide, C₁—C₂₀ alkoxy, siloxy, hydrocarbyl, ordialkylamido;

[0017] R, R′, and R″, which can be same or different, are selected fromhydrogen and C₁—C₂₀ hydrocarbyl;

[0018] and m+ n equals the valency of M minus 1.

[0019] The transition metal, M, may be any Group 3 to 10 metal or ametal from the lanthanide or actinide series. Preferably, the catalystcontains a Group 4 to 6 transition metal; more preferably, the catalystcontains a Group 4 metal such as titanium or zirconium.

[0020] When X is a C₁—C₂₀ hydrocarbyl group, it is preferably a groupthat lacks a hydrogen atom on a carbon that is beta to M. Thus,preferred hydrocarbyl groups include methyl, benzyl, phenyl, neopentyl,or the like.

[0021] Catalysts of the invention include a polymerization-stableanionic ligand, L. Suitable L ligands include cyclopentadienyl orsubstituted cyclopentadienyl anions such as those described in U.S. Pat.Nos 4,791,180 and 4,752,597, the teachings of which are incorporatedherein by reference. Suitable L ligands also include substituted orunsubstituted boraaryl, pyrrolyl, quinolinyl, and pyridinyl groups asdescribed in U.S. Pat. Nos. 5,554,775, 5,539,124, and 5,637,660, theteachings of which are also incorporated herein by reference. L can alsobe a substituted or unsubstituted azaborolinyl ligand, such as thosedescribed in PCT Int AppI. WO 96/34021. When multiple L ligands arepresent, they may be the same or different.

[0022] Suitable polymerization-stable anionic ligands include aminederivatives of the formula RR′N—A⁻ or RR′C═N—A⁻ wherein R, R′ and A areas described above. Thus, catalysts of the invention include ones havingmore than one amine derivative ligand.

[0023] The polymerization-stable anionic ligand L and the aminederivative ligand can be bridged. Groups that can be used to bridge thepolymerization-stable anionic ligand and the amine derivative include,for example, methylene, ethylene, 1,2-phenylene, and dialkyl silyls.Normally, only a single bridge is used in the organometallic compound.Bridging the ligand changes the geometry around the transtion metal andcan improve catalyst activity and other properties, such as comonomerincorporation and thermal stability.

[0024] A preferred catalyst comprises an activator and an organometalliccompound of the formula:

[0025] where

[0026] M is a Group 4-6 transition metal, preferably a Group 4 metal;

[0027] and L, X, R, R′, m, and n are as described above.

[0028] Preferably, X is chlorine, methyl, or benzyl.

[0029] Another catalyst of the invention comprises an activator and anorganometallic compound of the formula:

[0030] where

[0031] M is a Group 3-10 transition metal, preferably Groups 4-6 andmore preferably Group 4; and

[0032] A, L, X, R, R′, m, and n are as described above.

[0033] Preferably, X is chlorine, methyl, or benzyl.

[0034] A particularly preferred catalyst comprises an activator and anorganometallic compound of the formula:

[0035] where

[0036] Cp is a cyclopentadienyl ligand.

[0037] Suitable activators include alumoxanes. Preferred alumoxanes arepolymeric aluminum compounds represented by the cyclic formula(R⁴—Al—O), or the linear formula R⁴(R⁴—Al—O)_(s)AIR⁴ wherein R⁴ is aC₁—C₂₀ alkyl group and s is an integer from 1 to about 20. Preferably,R⁴ is methyl and s is from about 4 to about 10. Exemplary alumoxaneactivators are (poly)methylalumoxane (MAO), ethylalumoxane, anddiisobutylalumoxane. Optionally, the alumoxane activator is used with atrialkyl or triaryl aluminum compound, which preferably has the formulaAIR⁵ ₃ where R⁵ denotes a C₁—C₂₀ hydrocarbyl. MAO and mixtures of MAOwith other aluminum alkyls are preferred activators because they givehigh catalyst activity, good comonomer incorporation, and polymers withnarrow molecular weight distributions.

[0038] Suitable activators also include substituted or unsubstitutedtrialkyl or triaryl boron derivatives, such astris(perfluorophenyl)boron, and ionic borates such astri(n-butyl)ammonium tetrakis(pentafluorophenyl) boron or trityltetrakis(pentafluorophenyl) boron. The ionic borates ionize the neutralorganometallic compound to produce an active catalyst for olefinpolymerization. See, for instance, U.S. Pat. Nos. 5,153,157, 5,198,401,and 5,241,025, all of which are incorporated herein by reference.

[0039] The organometallic compound is prepared by any suitable method.Usually, the amine derivative is deprotonated with a strong base, andthe resulting anion is reacted with a transition metal complex to givethe organometallic compound.

[0040] In one convenient method, the amine derivative reacts withn-butyl lithium in an inert organic solvent (THF, toluene, diethylether, e g ) to give an amine derivative anion. Preferably, the solutionis concentrated The amine derivative anion is then preferably added to aslurry of the starting transition metal complex (e.g., cyclopentadienylzirconium trichloride) in an organic solvent as described above.Stoichiometric quantities are typically used. The reaction can occur atroom temperature, but a lower temperature of −100° C. to 0° C. ispreferred By-products are removed by filtration, the solvent isevaporated, and the organometallic compound is collected.

[0041] Preferably, the organometallic compound is used promptly afterpreparation because it may lose activity during storage. Storage of theorganometallic compound should be at a low temperature, such as −100° Cto 20° C.

[0042] It is preferable not to premix the organometallic compound andthe activator, as this may result in lower catalyst activity. Rather,the organometallic compound and activator are preferably injectedseparately into a reactor containing the monomer to be polymerized.Preferably, the activator is injected first. The molar ratio ofactivator to organometallic compound is preferably from about 1:1 toabout 15,000:1.

[0043] The organometallic compound and the activator may be used with asupport such as silica, alumina, magnesia, or titania. A support may berequired for some processes. For example, a support is generally neededin gas phase and slurry polymerization processes to control polymerparticle size and to prevent fouling of the reactor walls. In onemethod, the organometallic compound is dissolved in a solvent and isdeposited onto the support by evaporating the solvent. An incipientwetness method can also be used. The activator can also be deposited onthe support or it can be introduced into the reactor separately from thesupported organometallic compound.

[0044] The catalyst is particularly valuable for polymerizing olefins.preferably α-olefins. Suitable olefins include, for example, propylene.1-butene, 1-hexene, 1-octene, ethylene and the like, and mixturesthereof The catalyst is valuable for copolymerizing ethylene withα-olefins or di-olefins (e.g., 1,3-butadiene, 1,4-hexadiene,1,5-hexadiene).

[0045] The catalysts can be used in a variety of polymerizationprocesses They can be used in a liquid phase (slurry, solution,suspension bulk) high-pressure fluid phase, or gas phase polymerizationprocesses, or a combination of these. The pressure in the polymerizationreaction zones typically ranges from about 15 psia to about 15,000 psia,and the temperature usually ranges from about −100° C. to about 300° C.

[0046] Catalysts of the invention are highly productive. Typicalactivities range from 40 to 200 kilograms polymer per gram transitionmetal per hour, or higher (see Table 2 below). The catalysts incorporatecomonomers such as 1-butene well (see Example 5) and also producepolymers with narrow molecular weight distributions. Typical melt flowratios (MFR= MI₂₀/MI₂) range from about 10 to about 25. A MFR below 25indicates narrow molecular weight distribution and suggests improvedproperties characteristic of polymers made using a single-site catalyst.Typically, Zeigler-Natta catalysts yield polymers with MFRs of about 35.

[0047] The following examples merely illustrate the invention. Thoseskilled in the art will recognize many variations that are within thespirit of the invention and scope of the claims.

EXAMPLE 1

[0048] This example describes the synthesis of diethyl hydroxylaminecyclopentadienyl zirconium dichloride of the structural formula:

[0049] 1.6 M n-butyllithium in hexane (1.7 mL, 2.72 mmol) is added todiethylhydroxylamine (0.238 g, 2.67 mmol) dissolved in 10 mL oftetrahydrofuran at −78° C. After warming to room temperature, thismixture is added via cannula to a stirred slurry of cyclopentadienylzirconium trichloride (0.7 g, 2.67 mmol) and 30 mL of drytetrahydrofuran at −78° C. The reaction mixture is stirred an additional15 hours as the mixture warms to room temperature. The volatiles areremoved with vacuum and the resultant solid is isolated.

EXAMPLES 2-7

[0050] In these examples, ethylene is polymerized using the catalyst ofExample 1. The polymerization is conducted in a stirred 1.7-literstainless steel autoclave at 80° C. and 110° C. Dry, oxygen-free toluene(840 mL) is charged to the dry, oxygen-free reactor. MAO (10% intoluene, from Ethyl Corporation) is added by syringe without furtherpurification. The reactor is then heated to the desired temperature andsufficient ethylene is added to bring the reactor pressure to 150 psig.The reactor is allowed to equilibrate at the desired temperature andpressure. A solution of catalyst is prepared by dissolving 0.100 g ofthe catalyst of Example 1 in 100 mL of toluene, and the desired amountis added to the reactor.

[0051] After one hour, the ethylene flow is stopped and the reactor israpidly cooled to room temperature. The polymer is filtered, dried in avacuum oven, and weighed. Table 1 lists polymerization conditions, andTable 2 gives the results of the polymerizations.

[0052] The melt index of the polymer is measured according to ASTMD-1238, Condition E and Condition F. MI is the melt index measured witha 2.16 kg weight (Condition E). HLMI is the melt index measured with a21.6 kg weight (Condition F). The melt flow ratio (MFR) is defined asthe ratio of HLMI (or MI₂₀) to MI (or MI₂) and is a measure of molecularweight distribution. A MFR below 25 indicates narrow molecular weightdistribution and suggests improved properties characteristic of polymersmade using a single-site catalyst. Typically, a Zeigler catalyst yieldspolymer with a MFR of about 35. TABLE 1 Polymerization Conditions TempTime Hydrogen Catalyst AI/M Example (° C.) (min) (mmoles) Comonomer(mmoles) Activator (atomic) 2 80 60 0 None 0.018 MAO  494 3 80 60 0 None0.0073 MAO 1240 4 80 60 0 None 0.0018 MAO 4950 5 110  60 30  Butene,0.0018 MAO 4950 20 mL 6 110  60 30  None 0.0018 MAO 4950 7 110  60 0None 0.0018 MAO 4950

[0053] TABLE 2 Polymerization Results Wt. Catalyst PE Activity MI HLMIDensity Example (g) (kg/g Zr/hr) (dg/min) (dg/min) MFR (g/ml) 2 68.841.4 0.0430 0.736 17.3 — 3 69.6 105 0.0263 0.605 23.0  0.950 4 34.7 2090.0452 0.729 16.1  0.958 5 10.8 65.1 — — — >0.970 6 10.6 63.9 — —— >0.970 7 34.7 209 1.58  6.08  10.5  0.962

We claim:
 1. A catalyst which comprises: (a) an organometallic compoundof the formula:

wherein M is a Group 3-10 transition metal; A is O, S, N—R″, or P—R″; Lis a polymerization-stable anionic ligand; X is hydride, halide, C₁—C₂₀alkoxy, siloxy, hydrocarbyl, or dialkylamido; R, R′, and R″, which canbe same or different, are selected from hydrogen and C₁—C₂₀ hydrocarbyl;and m+ n equals the valency of M minus 1; and (b) an activator.
 2. Thecatalyst of claim 1 wherein L is a cyclopentadienyl. boraaryl, pyrrolyl,azaborolinyl, quinolinyl, or pyridinyl group, or is another aminederivative of the formula: RR′N—A⁻ or RR′C═N—A⁻.
 3. The catalyst ofclaim 1 wherein M is a transition metal of Groups 4 to
 6. 4. Thecatalyst of claim 3 wherein M is a Group 4 transition metal.
 5. Thecatalyst of claim 4 wherein X is a chlorine, methyl or benzyl.
 6. Thecatalyst of claim 1 wherein the activator is an alumoxane.
 7. Thecatalyst of claim 6 wherein the activator further comprises a trialkylor triaryl aluminum compound.
 8. The catalyst of claim I wherein theactivator is a trialkyl or triaryl boron compound or an ionic borate. 9.A supported catalyst of claim 1 .
 10. A catalyst which comprises: (a) anorganometallic compound of the formula:

wherein M is a Group 4-6 transition metal; L is a polymerization-stableanionic ligand; X is hydride, halide, methyl, phenyl, benzyl, neopentyl,or a C₁—C₂₀ alkoxy, siloxy, or dialkylamido; R, R′, and R″, which can besame or different, are selected from hydrogen and C₁—C₂₀ hydrocarbyl andm+ n equals the valency of M minus 1; and (b) an activator.
 11. Thecatalyst of claim 10 wherein L is a cyclopentadienyl, boraaryl,pyrrolyl, azaborolinyl, quinolinyl, or pyridinyl group, or is anotheramine derivative of the formula: RR′N—A⁻ or RR′C═N—A⁻.
 12. The catalystof claim 11 wherein M is a Group 4 transition metal.
 13. The catalyst ofclaim 12 wherein X is a chlorine, methyl, or benzyl.
 14. The catalyst ofclaim 10 wherein the activator is an alumoxane.
 15. The catalyst ofclaim 14 wherein the activator further comprises a trialkyl or triarylaluminum compound.
 16. The catalyst of claim 10 wherein the activator isa trialkyl or triaryl boron compound or an ionic borate.
 17. A supportedcatalyst of claim 10 .
 18. The catalyst of claim 10 wherein theorganometallic compound has the structure:

wherein Cp is a cyclopentadienyl ligand.
 19. A catalyst which comprises:(a) an organometallic compound of the formula:

wherein M is a Group 3-10 transition metal; A is O, S, N—R″, or P—R″; Lis a polymerization-stable anionic ligand; X is hydride, halide, C₁—C₂₀alkoxy, siloxy, hydrocarbyl, or dialkylamido; R, R′, and R″, which canbe same or different, are selected from hydrogen and C₁—C₂₀ hydrocarbyl,and m+ n equals the valency of M minus 1; and (b) an activator.
 20. Thecatalyst of claim 19 wherein L is a cyclopentadienyt, boraaryl,pyrrolyl, azaborolinyl, quinolinyl, pyridinyl group or another aminederivative of the formula: RR′C═N—A⁻.
 21. A method which comprisespolymerizing an olefin in the presence of the catalyst of claim 1 . 22.The method of claim 21 wherein the olefin is ethylene or a mixture ofethylene and another olefin.
 23. A method which comprises polymerizingan olefin in the presence of the catalyst of claim 10 .
 24. The methodof claim 23 wherein the olefin is ethylene or a mixture of ethylene andanother olefin.
 25. A method which comprises polymerizing an olefin inthe presence of the catalyst of claim 19 .
 26. The method of claim 25wherein the olefin is ethylene or a mixture of ethylene and anotherolefin.